There is little support if wearing a regular lifting belt in the loose way, that most do. If you can slide one finger between the belt and the body, you are wearing it the wrong way. A lifting belt was made to be worn extra tight, for single to 3 rep max on heavier lifts. Which required lower to mid-range back involvement. Lifting belts seem to be one of the most misunderstood of gym/lifting equipment.
For these heavier lifts the belt should be drawn and cinched as tight as possible. This will put great pressure on the ab wall and internal organs and may raise the blood pressure, as well as limiting the breathing abilities. Main reason they should only be worn for a very short period. Watch a PL'er cinch up, with the help of another guy, before a major lift... super tight (one of the reasons that some PL'er will walk towards a DL bar like they have a iron rod up their butts)
If desiring a lifting belt, than it shouild be custom designed for your body type. Always try one on before buying, to get the proper feel. Might suggest the wider, rather than the narrow, type backing. Use caution if buying one on line, just because it might look cool in the picture ad's. Remembering that a good quality lifting belt is for the serious lifer, not the average gym rat. And can cost quite a bit of money for the investment of a good and long lasting one.
If using a regular OTC lifting belt, than try folding a thicker towel and placing it between the back and belt. A towel will tend to follow the curve of the back for better support, if drawn tight enought. Works better on a wider belt. Even custom design belts seem to improve a bit, with the towel thing. Could never quite get why some wear those narrow type belts, probably for vanity reasons. Good Luck.
Side Bar: Want a stronger back and avoid some potential injuries, than you might focus on working the upper & lower ab's wall (and obliques, at times) with heavier resistence. Treat the reps in the 6-9 range. A powerfull set of ab's can be a counter balance to a stronger back, doing away with any weaker link within the center of the body. No useless marathon ab workout is ever required, just heavier attention to the ab's.